Process for the production of arc-light electrodes



25 erto employed, was,

i 35 in the moulding 'of the Patented Dec. 27,1927.

4UNI'I'ED STATES Lnororm zam., or BERLIN-Damian,

TIENGESELLSGHAFT, ABTEIL'UNG PL GERMANY,

Assreron 'ro nrennswnnxn Ax- ANIAWERKE, or BERLIN, GERMANY.

PROCESS FOR THE PRODUCTION OF ARC-LIGHT ELECTRODES.

Application ied May 31, 1923, Serial No. 642,670,

Arc-light electrodes have .hitherto been manufactured by intimately mixing carbonaceous material, such as coke, soot, retort graphite, or the like, with a binding agent 5 such, for example, as tar oil, tar, syrup, starch, and the like, in mixing machines. After being mixed the material is kneaded in edge-mills or calenders in order to obtain as uniform and plastic aconsistency as possible. The mass obtained is then by preliminary compression formed into balls or masses, which are of such cross-section that they will subsequently tit into the cylinder of a hydraulic press.

pression is effected either in ordinary presses or in hydraulic resses. The ball or mass is then put into t e cylinder of a hydraulic press and extruded through a mouth-piece, the opening of which is of the same shape as the finished-carbon. The raw carbon is then finished and afterwards burnt in order to carbonize the binding agent, and is then ready for sale. f

This method, which has been the one hithhowever, attended by a number of disadvantages. Even with the most intimate working up of the raw materials it was impossible by this method to remove 'air imprisoned I)inthe mass. The

material was plastic and possessed all the properties of a true iiuid-p-that is to say, its volume increased upon relaxation of the pressurein accordance with its increasing elasticity. This was particularly manifest carbon in the hydraulic press. Further, the density of the compressed mass could not be increased by a given pressure, as the elasticity of the mass acted in opposition to the pressure and the 40 article extruded from the mouth-piece was of greater cross-section than the mouthpiece itself. The carbon makers, however, sought to make the carbon more dense an'd less porous, as upon the density of the carbon notonly depends the combustion thereof, but also (in the case of the so-called hol mogeneous eEect-carbons that contain the illuminating salts intimately disseminated throughout the wh'ole transverse section) the radiation of the light. It has therefore also been suggested not to eXtr-ude carbons or electrodes in the form of a cord or string from an extruding press but to press them separately in moulds; and it has also been `suggested to press the raw carbon extruded The preliminary com- 'and in Germany June 9, 1922.

from an hydraulic press in the form of a cord in a mould.

Both these methods are, however, not only very uneconomical, as pressing in moulds is expensive and takes up much time, but they also suffer from the disadvantage that the openings which are provided in the moulds for the escape of air and gases become very easily choked up, whereby the object aimed at, namely that of making the electrodes 0r carbons denser, cannot be attained.

These disadvantages are overcome according to the present invention by the fact that in the preparation of the raw material it is made at the very commencement as dense as it is possible to make it and this density is increased at each further operation. This is attained in the iirst instance by a complete removal of the air from the crude mass, which is eiiected by compression of the masses or balls thereof, while the masses or balls are subjected to a vacuum. By such means the mass or masses are deprivedof air and are also compressed or consolidated. This mass from which the air has been thus removed is then ejected from the press and rolled out as thinly as possible on ca'lendcrs. The rolled-out thin layers are then superposed and again subjected to mechanical pressure under a vacuum the mass being simultaneously given the form of the lumps which fit the moulding cylinder. The crude mass or the masses produced in the respecv tive stages of the process may be subject to compression in any type of' press, it being only necessary that the mould space inwhich the mass to be compressed is passed should be put into communication as by means of a pipe with a vacuum pump or a vessel in which a vacuum is maintained. The accompanying drawing illustrates diagrammatically such a press in which the mass to be deprived of air and to be compressed is placed within a cylinder b in which operates the plunger of an hydraulic press with power cylinder ka. In the operation of the press the mass .is subjected to pressure by the plunger on movement of the piston within the power cylinder a and simultaneously the mass' is subjected to a vacuum exerted through the pipe f by the vacuum pump d. A'pressure pump 0 is also connected to the cylinder b by the pipe e and is advantageously employed to apply iuid pressure to the moulded mass upon the completion of the movement and the retraction of the plunger ,'fo facilitate the removal of the moulded mass.

he ipes e and f are provided with closure mem ers g and 7L respectivelyfor the control of the action of the pipes d and c as desired. The simultaneous use of a vacuum and mechanical pressure also enables the amount of binding agent requisite to be reduced, thereby likewise increasing the strength of the product. In this way the masses or balls are deprived of a portion of their elasticity, and it is now possible to use in the hydraulic extrusion press pressures which have hitherto been impossible in the production of artificial carbons. The subsequent process of treatment employed is carried out in the usual way, but it is advisable, in order to render the carbon still denser, to impregnate it before burning with tar oil in the usual way'under vacuum and pressure, whereby the last remaining pores become filled up with tar coke when the carbons are subsequently burned. Suitable means for the purpose are described b V Dr. Julius Zellner in his book Die knstlichen Kohlen fr elektrotechinische und elektrochemische Zwecke, ihre Herstellung und Prfung (published by Julius Springer, Berlin 1903). f

Instead of the tar now commonly em` ployed colloidal carbon may be employed both in the preparation of the mixture and also in the impregnation of the crude carbon which enables a minimum amount of binding agent to be used.

I claim: 1. A process for the manufacture of carbon electrodes for arc-lighting consisting in subjecting a plastic mass of raw material and inding agent to compression in a vacuum, then moulding bodies in the form of electrodes from the mass thus treated, and then subjecting-the said bodies to burning, substantially as described.

2. A process for the manufacture of carbon electrodes for arc-lighting consisting in subjecting a plastic mass of raw material and binding agent repeatedly to compression in a vacuum, the compressed mass being broken down between successive stages of compression and moulding bodies from the mass produced, in the form of electrodes, substantially as described.

process for the manufacture of carbon electrodes for arc-lighting consisting in subjecting a plastic mass of raw material and binding agent to compression in a vacuum, then rolling out the mass produced into thin layers and then again compressing the mass ro'lled out, substantially as described.

4. A process for the manufacture of carbon electrodes for arc-lighting consisting in subjecting aplastic mass of raw material and binding agent to compression in a vacuum, impregnating the mass with a filling substance vsuch as tar oil under vacuum and pressure, then moulding the plastic mass into the form of bodies adapted for use as electrodes, and then subjecting the said bodies to burning, substantially as described.

5. A process for the manufacture of car bon electrodes for arc-lighting consisting in subjecting a plastic mass of raw material and binding agent to compression in a vacuum, then rolling out the mass produced into thin layers and then subjecting the mass so treated to further compression in a vacuum and then moulding from the mass produced bodies in the form of electrodes, substantially as described.

LEOPOLD KAHL. 

